<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .fa{
            width: 400px;
            margin-bottom: 30px;
            border: 1px solid red;;
        }
        .son{
            width: 0px;
            height: 40px;
            background-color: #f0f;
            text-align: center;
            line-height: 40px;
        }
    </style>
</head>
<body>
    <div class="fa">
        <div class="son">
            <span>0</span><span>%</span>
        </div>
    </div>
    <button id="but">安装</button>
    
    <script>
        // 逻辑：1.利用定时器来进行递增操作（width、百分数）
        // 2.当变量 达到400px时，是停止定时器
        let but = document.getElementById('but');
        let div = document.getElementsByTagName('div');
        let span = document.getElementsByTagName('span');
        let timer = null;
        but.onclick = function(){
            let num = 0;
            if(timer==null){
                timer = setInterval(()=>{
                    num +=1;
                    // 给宽进行递增
                    div[1].style.width = num+'px';
                    // 给百分比递增
                    span[0].innerText = Math.ceil(num/400*100);
                    if(num==400){
                        clearInterval(timer);
                    }
                },10);
            }
            
        }

    </script>
</body>
</html>